It really depends on what part is creaking, but somewhere there’s a gap near the creak between the joist, subfloor, and/or floor that’s letting things flex. Gotta close that gap to stop the squeak.

So for troubleshooting purposes, I would suggest disconnecting the interconnect wire, but leaving them powered. You’ll want to reference the user guide for how to hook them up as a single station and do that. Then you can see which one is actually giving the fault.

If none of them trigger, then the problem’s probably in the wiring. Reconnect half of them and see if it happens again. Switch halves if it doesn’t, reduce by half if it does. Keep going until you find the connection causing it.

Keep in mind that you’ll still want the interconnect wire intact, so make sure to connect the ends together in the bays of the alarms you’re disconnecting from the interconnect network.

My state’s 811 (PA One Call) has a list of private line surveyors on their site for this exact situation. Maybe start with your state or local government and see if they have recommendations?